Universal donors have which type of blood?

Universal donors have blood type O. This is due to the absence of A and B antigens on the surface of their red blood cells. When individuals with type O blood donate, their blood can be transfused into patients with any of the other blood types—A, B, AB, or O—without the risk of agglutination (clumping) that can occur if a recipient has blood that carries opposing antigens.

Type O blood is considered universal for this reason. The immune response can recognize the absence of these antigens as neutral, thus allowing the blood to mix with any recipient’s blood type safely. In contrast, blood types A, B, and AB all carry specific antigens, which can provoke an immune response in individuals who do not possess those antigens. Therefore, the unique characteristics of type O blood make it the safest choice for blood transfusions across various blood groups.